Read more: “Unnatural selection: How humans are driving evolution“
In Finland, the tawny owl used to be mainly grey. But since the 1960s, the proportion of a brown subtype has risen fast. “The frequency averaged around 12 per cent in the early 60s and has increased steadily to over 40 per cent nationwide,” says Patrik Karell of the University of Helsinki, whose findings were published earlier this year (Nature Communications, DOI: 10.1038/ncomms1213).
His team found that grey owls (pictured above right) have an advantage over brown ones only when there is lots of snow. As winters have become milder, the brown subtype has thrived. It is possible that this is because brown owls are better camouflaged when there is less snow, but it could also be because brown coloration is linked to another characteristic, such as higher energy needs.
There are countless examples of how global warming is affecting life, from plants flowering earlier in spring, to species spreading to areas that were once too cold for them to survive, to birds becoming smaller. The vast majority of these changes are not genetic but due to plasticity: organisms’ built-in ability to change their bodies and behaviour in response to whatever the environment throws at them. At least a few species, however, like the owls of Finland, are already changing genetically – evolving – in response to climate change.
In North America, for instance, pitcher plant mosquitoes lay their eggs in pitcher plants and the larvae enter a state of dormancy in the winter months before resuming development in spring. Dormancy is genetically programmed, triggered not by falling temperature but by the ...